Polyamide resin compositions reinforced with fibrous reinforcing materials such as glass fiber and carbon fiber or inorganic fillers such as calcium carbonate are widely known. However, since these reinforcing materials have poor affinity to polyamide, the reinforced polyamide resin compositions have reduced toughness while mechanical strength and heat resistance are improved. Further, molded articles of a fiber-reinforced polyamide resin composition suffer from appreciable warp. Additionally, in using the inorganic fillers, substantial improvement in mechanical strength or heat resistance cannot be obtained unless they are added in a large quantity.
In order to eliminate these disadvantages of conventional reinforced polyamide resin compositions, a composition comprising polyamide resin and silicate layers dispersed in the polyamide resin on the molecular level by introducing polyamide chains into the laminae of a layered silicate has been proposed. Examples of such compositions are disclosed in the specifications of U.S. Pat. No. 4,739,007 in the case of using polyamide and montmorillonite, and U.S. Pat. No. 5,414,042 in the case of using polyamide and fluoromica-based minerals.
Although its mechanical properties, heat resistance and warp when molded are improved, the above-described composition, when converted into films or fibers, still suffers from insufficient tensile elongation and poor transparency due to the high crystalinity of nylon 6 which is typically used as a matrix.
A polyamide resin composition for film comprising copolyamide resin and 0.05 to 1.5 wt % of a layered silicate dispersed in the resin has been proposed (in unexamined Japanese patent No. 5-339498) to obtain excellent transparency and surface gloss. However, the transparency of the composition is not adequate and the dispersion of layered silicate in the copolyamide is not considered to be at a molecular level. This is because the polyamide resin composition is obtained by mixing or kneading a copolyamide and a layered silicate.